This invention relates to a color cathode ray tube, and more particular to a color cathode ray tube equipped with an improved base which is attached to a neck section, wherein power saving and high resolution with reduced power consumption can be realized.
In general, in color cathode ray tubes, a panel and a funnel constitute an envelope, and an electron gun assembly is provided in the funnel""s cylindrical neck. Three electron beams emitted from the electron gun assembly are deflected by a magnetic field generated from a deflecting yoke that is mounted on the outer surface of the funnel, and are directed, via a shadow mask, to a phosphor screen provided on the inner surface of the panel. The phosphor screen is thus horizontally and vertically scanned by the three electron beams, thereby displaying a color image thereon.
At present, the color cathode ray tubes constructed as above are mainly of an inline type, in which three electron beams emitted from the electron gun assembly are arranged in line to pass in a single horizontal plane.
The electron gun assembly generally has three cathodes, three heaters each for heating a corresponding one of the three cathodes, and a plurality of electrodes provided between the cathodes and the phosphor screen. These heaters, cathodes and electrodes are fixed integrally as one body by an insulating support bar.
In the electron gun assembly, an electron beam generating section is formed of the cathodes and first and second electrodes adjacent thereto in this order, while a main lens section for converging, onto the phosphor screen, electron beams emitted from the electron beam generating section is formed of a plurality of electrodes located between the first and second electrodes and the phosphor screen.
In the electron gun assembly constructed as above, a plurality of stem pins are airtightly inserted through a flare section of a stem welded to an end portion of a neck, and the cathodes are supported by predetermined stem pins, thereby housing the electron gun assembly in the neck. Further, in order to apply necessary voltages for forming the electron beam generating section and the main lens section, the stem pins are connected to the heaters, the cathodes, and the electrodes other than a final accelerating electrode that cooperates with a focusing electrode to form a main lens for finally converging electron beams onto the phosphor screen. A relatively high voltage that is 20-40% of an anode high voltage applied to the final accelerating electrode is generally applied, via the stem pins, to the focusing electrode, which cooperates with the final accelerating electrode to form the main lens. A voltage lower than the voltage applied to the focusing electrode is applied to the heaters, the cathodes and the electrodes other than the focusing electrode and the final accelerating electrode.
In general, the performance of the electron gun assembly is expressed by lens constants such as lens magnification power, spherical aberration, etc. These two constants, in particular, substantially determine the performance of the main lens. The lower the lens constants, the higher the performance of the main lens section, the greater degree the electron beam is converged, and the smaller the beam spot on the screen, which means the higher the resolution.
However, the resolution of color cathode ray tubes is influenced by a magnetic field generated by their deflecting yokes, as well as the performance of the main lens sections of their electron gun assemblies. In the case of inline-type color cathode ray tubes as described above, self-conversion inline type color cathode ray tubes are widely put to practical use, in which three electron beams arranged in line to pass in a single horizontal plane are converged on any point of the entire screen, with a horizontally deflected magnetic field and a vertically deflected magnetic field generated by the deflecting yoke in the shape of a pin cushion and a barrel, respectively. In these color cathode ray tubes, a non-uniform magnetic field, which consists of the pin-cushion shaped horizontally deflected magnetic field and the barrel-shaped vertically deflected magnetic field, will distort the beam spot in a manner such that at a peripheral portion of the screen, the beam spot has a horizontally long core portion of a high luminance and a halo portion of a low luminance extending vertically relative to the core portion. Thus, the resolution is degraded.
As means for eliminating distortion in beam spot due to the non-uniform magnetic field, there is provided a dynamic focusing electron gun assembly, in which a voltage that increases in synchronism with the deflection of electron beams is applied to some of the electrodes in the electron gun assembly, thereby forming a non-symmetrical lens whose power varies in accordance with the deflection of the electron beams to eliminate distortion in beam spot.
In this electron gun assembly, however, it is necessary to add at least one electrode to the electrodes employed in a usual electron gun assembly, and also to add at least one stem pin to those required for the usual electron gun assembly.
On the other hand, to save power required for the color cathode ray tubes, it is desired to reduce the power consumption of their deflecting yokes that consume the greatest power. To this end, it is effective to make a deflection coil approach the electron beams for enhancing its sensitivity for deflection, and hence effective to reduce the outer diameter of the neck on which the deflecting yoke is mounted, so that Lorentz""force caused by the deflected magnetic field of the yoke can be efficiently applied to the electron beams.
At present, the color cathode ray tubes have several standards of nominal neck outer-diameters ranging from 22.5 mm to 36.5 mm, and 29.1 mm is mainly employed. To save the power consumption of the color cathode ray tubes, it is effective to set the neck outer-diameter at 22.5 mm. However, in the case of the stem sealed by a neck with an outer diameter of 22.5 mm, the flare section welded to the neck has a small diameter, and the number of stem pins, which are airtightly inserted circumferentially through the flare section, is 8 that is the minimum number required in each color cathode ray tube. It is considered difficult to increase the number of the stem pins in light of the withstand voltage between them.
In other words, it is very difficult to enhance the resolution of the color cathode ray tube and at the same time to reduce its power consumption.
As means for simultaneously realizing high resolution and power saving, a structure is proposed, in which stem pins are bent within the flare section of a stem designed for a neck with an outer diameter of 22.5 mm, thereby enabling the formation of a pin circle, using outer pins (i.e. outer portions of the stem pins) extending outside the flare section, to have a diameter of 15.24 mm that is equal to the diameter employed in a stem designed for a neck with a diameter of 29.1 mm. By virtue of this structure, the number of the stem pins can be increased.
Concerning the withstand voltage of the stem in the above structure, the outer pins located in the outside atmosphere that contains moisture must be considered. However, there is no problem among the outer pins, since the pitch of the outer pins is same as that of the conventional neck structure with 29.1 mm in the conventional color cathode ray tube. There is almost no problem among inner leads (i.e. inner portions of the stem pins) located in a vacuum atmosphere within the tube. This means that degradation in withstand voltage can be avoided.
Even in the above structure, a base designed for a neck with an outer diameter of 29.1 mm is used as a base to be adhered to the outer surface of the stem for protecting the stem pins, in light of the combination of a socket incorporated in a display unit such as an image receptor, i.e. to secure compatibility with a usual color cathode ray tube. However, in the case of employing the base designed for a neck with an outer diameter of 29.1 mm, the maximum outer diameter RB max around the tube axis is 25.0 mm (radius: 12.5 mm) as shown in FIG. 1. To attach this base, the deflecting yoke to be mounted on the outer surface of the funnel from the neck end side must have a minimum coil diameter of 25.0 mm or more, which means that a gap will be defined between the coil and the neck with the outer diameter of 22.5 mm. Accordingly, even if the neck outer diameter is reduced as described above, sufficient power saving cannot be realized.
As aforementioned, there is a dynamic focusing electron gun assembly, in which a voltage that increases in synchronism with the deflection of electron beams is applied to part of the electrodes included in the electron gun assembly, thereby forming a non-symmetrical lens whose power varies to eliminate distortion in beam spot which may be caused by a non-uniform magnetic field generated from the deflecting yoke. However, in this electron gun assembly, it is necessary to add at least one electrode to the electrodes employed in a usual electron gun assembly, and also to add at least one stem pin to those required for the usual electron gun assembly.
On the other hand, to save power required for the color cathode ray tubes, it is effective to reduce the neck outer diameter to make the deflection coil approach electron beams. If, however, the neck outer diameter is set at 22.5 mm that is the minimum value among the presently standardized values, the number of stem pins employed in the stem for the neck with the outer diameter of 22.5 mm is only 8. To increase the number of the stem pins is difficult in light of the withstand voltage between them.
In other words, it is very difficult to enhance the resolution of the color cathode ray tube and at the same time to save its power consumption.
As means for simultaneously realizing high resolution and power saving in the color cathode ray tube, a structure is proposed, in which the neck outer diameter is set at 22.5 mm, and stem pins are bent within a flare section of a stem designed for the neck with the outer diameter of 22.5 mm, thereby enabling the formation of a pin circle, using the outer pins extending outside the flare section, to have a diameter of 15.24 mm that is equal to the diameter employed in a stem designed for a neck with a diameter of 29.1 mm. By virtue of this structure, the number of the stem pins is increased.
In the above structure, a base designed for a neck with an outer diameter of 29.1 mm is used as a base to be adhered to the outer surface of the stem for protecting the stem pins, in order to secure compatibility with a socket that is to be connected to the base of a usual color cathode ray tube. This base, however, has a diameter of 25.0 mm larger than the outer diameter of the neck. Further, to attach this base, the deflecting yoke to be mounted on the outer surface of the funnel from the neck end side must have a minimum coil diameter of 25.0 mm or more, which means that a gap will be defined between the coil and the neck. Accordingly, even if the neck outer diameter is reduced, sufficient power saving cannot be realized.
This invention has been developed to solve the above-described problems, and is aimed at constructing a color cathode ray tube capable of realizing high resolution, with its power consumption reduced by the employment of a small neck outer diameter.
The invention provides
(1) A color cathode ray tube comprising:
a vacuum envelope including a substantially cylindrical neck, a funnel having an extended portion extending from the neck, and a panel coupled to the funnel;
an electron gun assembly located in the neck and having cathodes, heaters for heating the cathodes and a plurality of electrodes for focusing electron beams emitted from the cathodes;
a stem including a plurality of stem pins connected to the cathodes, the heaters and predetermined ones of the electrodes, and a flare section welded to an end of the neck, the stem pins being airtightly inserted circumferentially through predetermined portions of an outer surface of the flare section of the stem such that the predetermined portions form a reference circle; and
a base adhered to the flare section of the stem and having stem-pin inserting holes through which the stem pins are inserted,
wherein the neck has an outer diameter of from 22 mm to 23 mm, the reference circle formed by the stem pins on the outer surface of the flare section is set at a pin circle with a nominal diameter of 15.24 mm, and the base has a diameter not more than a maximum diameter of 23 mm.
(2) In the color cathode ray tube specified in item (1), the electron gun assembly is of a dynamic type in which a voltage that varies in synchronism with the deflection of the electron beams emitted from a deflecting yoke is applied to at least one electrode selected from the plurality of electrodes, the voltage that varies in synchronism with the deflection of the electron beams being applied via at least one of the stem pins.
(3) In the color cathode ray tube specified in item (1), the number of the stem pins is not less than 9.
(4) In the color cathode ray tube specified in item (1), partitions radially extend on a surface of the base opposite to a surface thereof adhered to the stem, and partition those of the stem pins connected to those of the electrodes to which a relatively high voltage is applied, from those of the stem pins connected to those of the electrodes, to which a relatively low voltage is applied.
(5) In the color cathode ray tube specified in item (4), the partitions extend across the pin circle of the stem pins to an outer edge of the base.
(6) In the color cathode ray tube specified in item (4), the radial partitions extend across the pin circle of the stem pins to an outer edge of the base, and include a circumferential partition that partitions, together with the radial partitions, those of the stem pins connected to those of the electrodes to which the relatively high voltage is applied, from those of the stem pins connected to those of the electrodes, to which the relatively low voltage is applied.
(7) In the color cathode ray tube specified in item (6), the circumferential partition has a height lower than the radial partitions that extend across the pin circle of the stem pins to the outer edge of the base.
(8) In the color cathode ray tube specified in item (6), the circumferential partition extends along the outer edge of the base.
(9) In the color cathode ray tube specified in item (4), the partitions extend across the pin circle of the stem pins to an intermediate portion between the pin circle and the outer edge of the base.
(10) In the color cathode ray tube specified in item (4), the partitions have a height greater than a length of the stem pins that extend to an outside of the base.